Drop events, overzise packets and pause frames

Hi,

We have a customer that has alot of issues with the wireless network.

when i log into the switch (Dell N1548POE) and check RMON statistics i can see that there is alot of "drop events", oversized packets and alot of pause frames recived. is there anyway that I can fix this or should it be like this?

The customers setup:

Fortigate 100D (v5.4.4)

4x FortiAP 221C (v5.4-build0354)

1x FortiAP 321C (5.4-build0354)

1x Dell Networking N1548

1x Dell Networking N1548 POE

there is about 50-60 devices on the wifi networks(4 diferent SSID/networks), all SSID's is on local bridge(vlan)